Needed to ranibow up my partner's bike, so I snagged these. they're clear plastic, maybe polycarbonate, with a step-tooth design that adjusts the height as ro rotate different square teeth into engagement. the have little anti-slide nubs on each tooth that fit into an opposite recess and lock the teeth in place. I was doing a 1" to 1-1/8" conversion, so I slipped a polished alloy shim behind these spaces and it looks fantastic! they really stand out at a distance. with black behind them, they would be muted but still visible. cheap, too! A+